1. Field of the Invention
The invention relates to a primary transmission for high rpm (revolutions per minute) motors for auxiliary drive units, wherein an eccentric disc is connected to the drive shaft of the motor so as to rotate with the drive shaft and has supported thereon a spur gear which acts as a first drive member. The outer toothing of the spur gear engages at a location of engagement an inner toothing of a stationarily secured internal ring gear arranged concentrically to the drive shaft. The number of teeth of the spur gear is reduced by at least one relative to the number of teeth of the internal ring gear. The diameter of a circle about the ends of the teeth of the spur gear is smaller by at least one tooth height than the diameter of the circle at the base of the teeth of the internal ring gear. The eccentric throw of the eccentric disc relative to the center of the drive shaft corresponds to half the difference of the diameters of the circle about the ends of the teeth of the spur gear and of the circle about the base of the teeth of the internal ring gear. The spur gear is coupled in a torque-transmitting manner with a driven disc forming a second drive member and concentrically supported relative to the drive shaft. One of the drive members has at least one axially projecting pin which engages a bore of the other drive member, and the bore has a diameter which is greater by the amount of the eccentric throw of the eccentric disc than the diameter of the pin of the former drive member.
2. Description of the Related Art
Primary transmissions with a high reducing rate can be realized on motors especially by employing worm gears. The use of a worm gear, in general, also has the advantage of providing a self-locking action, but is not possible in all cases because an angular drive arrangement results for which there is not enough space available in some situations.
A transmission with high reducing rate is also possible by employing an open planetary gear system in which the planet gear is embodied as a spur gear supported on an eccentric member providing the transmission stay and meshing with a hollow gear at an engagement location. Such a transmission with high reducing rate and self-locking action is, for example, known from U.S. Pat. No. 3,673,891. This patent relates to the use of a rotary movement introduced into a pivot shaft having a fixedly connected eccentric disc for the purpose of pivoting the back rest of a vehicle seat. Similar conditions are also present in a solution disclosed in the U.S. Pat. No. 3,667,804. In this case, there is also a manually actuated drive shaft with a fixedly connected eccentric disc on which a spur gear is supported whose outer toothing meshes with the inner toothing of a stationarily secured ring gear. In the disclosed embodiment, the internal ring gear is a component of a mounting of a seat portion. The spur gear has at one end face thereof three projecting pins which engage bores at the mounting connected to the back rest wherein these bores have an inner diameter which is larger by the amount of the eccentric throw than the outer diameter of the pin. Also, the diameter of the circle extending about the ends of the teeth of the spur gear is smaller by at least one tooth height than the diameter of the circle about the base of the teeth of the internal ring gear. Also, the number of teeth of the spur gear is smaller than the number of teeth of the inner toothing of the internal ring gear. The mounting which is connectable to the back rest pivots exactly about the center point of the pivot shaft because the eccentric movement overlying the rotary movement of the spur gear is compensated completely by the pins engaging the bores in the mounting and having a smaller diameter than these bores. In this prior art configuration which is also a self-locking embodiment, the pivot shaft is manually driven by a hand wheel connected fixedly to the pivot shaft, but it is conceivable to connect the pivot shaft to an electric motor. However, centrifugal forces will result for high rpm motor drives due to the off-center mass arrangement of the eccentric disc which will result in disruptive imbalance.
It is an object of the present invention to provide a space-saving, motor-driven primary transmission with high reducing ratio in which the mass forces resulting from the imbalances can be compensated by means which are identical to the components serving to transmit the torque.
In accordance with the present invention, this is achieved in that axially adjacent to the eccentric disc supporting the spur gear at least one further eccentric disc identical to the first eccentric disc is provided which ensures mass compensation and which is fixedly coupled to the drive shaft of the motor in such a way that the eccentric throws of the eccentric discs are positioned diametrically opposite one another.
By arranging a second eccentric disc with diametrically oppositely positioned eccentric throw, a second centrifugal force results which counteracts the centrifugal force of the first eccentric disc. Accordingly, the mass forces cancel one another so that even at high rpm at the motor drive shaft quiet running condition of the drive shaft will result. The eccentric discs are both of the same configuration. A primary transmission configured in this way is also self-locking.
For realizing support advantages of the drive shaft, on the one hand, and further mass compensation, on the other hand, a second spur gear is supported on the second eccentric disc. This spur gear also engages the inner toothing of the internal ring gear and acts as a transmission member between the drive members. On the one hand, it has at least one receiving bore for receiving the axially projecting pins of the first drive member and, on the other hand, it has at least one axially projecting pin for engaging a receiving bore of the second drive member in the form of a driven disc.
Even though it is possible to provide a combination of only a single pin at the spur gear and only a single bore at the driven disc for torque transmission, it is advantageous according to the features of the invention to provide the first drive member in the form of the spur gear with several axially projecting pins that are distributed uniformly on a circle which is coaxial to the bearing location of the spur gear and to provide the same number of receiving bores in the driven disc forming the second drive member. The receiving bores are arranged on a circle of the same size as that one on which the pins are arranged. However, the circle on which the bores are arranged is coaxially positioned to the bearing projection of the driven disc supported coaxially relative to the drive shaft in the transmission housing. This holds also true when employing a transmission member which is positioned between the drive members and is in the form of a spur gear. In this case, several axially projecting pins are arranged uniformly on a circle coaxial to the bearing location of the spur gear forming the first drive member. The axially projecting pins engage the same number of receiving bores in the second spur gear forming the transmission member between the drive members. Several pins arranged between the receiving bores project axially from this transmission member and engage corresponding receiving bores of the driven disc supported coaxially to the drive shaft. For the purpose of reducing friction or running noise, it may be advantageous to surround the pins with anti-friction bearings, e.g. plain bearing bushings or roller bearings, which roll on the inner circumference of the receiving bores which are larger by the amount of the eccentric throw than the outer diameter of the bearing bushings or roller bearings, i.e., the pin diameter includes the respective bearing. Moreover, for reducing noise and for ease of running, it may be advantageous to surround the pins with elastic intermediate rings which then receive the plain bearing bushings or roller bearings.